This invention relates to disposable diapers for absorption and containment of excrement.
Japanese Patent Publication No. 1977-20692A disclosed several embodiments of a body fluid absorbent core used in a sanitary napkin, each comprising fluff pulp fibers and super-absorbent polymer particles. These embodiments include the core comprising the super-absorbent polymer particles and the fluff pulp fibers homogeneously mixed together and the core comprising a layer of aggregated super-absorbent polymer particles and two layers of fluff pulp fibers sandwiching the layer of polymer particles from above and below, respectively.
It is well known that a water holding capacity of the super-absorbent polymer particles is substantially higher than a water holding capacity of fluff pulp fibers and use of the super-absorbent polymer particles is effective to prevent a so-called rewet phenomenon. However, once having formed a gel block, the super-absorbent polymer particles may have an effect opposite to what was expected for these polymer particles. To avoid this, it is preferred for the core comprising a mixture of the super-absorbent polymer particles and the fluff pulp fibers to mix them together as homogeneously as possible and thereby to prevent the individual super-absorbent polymer particles from coming in contact one with another. To this end, however, a problem is faced that a content of the super-absorbent polymer particles in the core should be inevitably limited. As one of measures to solve this problem, it is well known to use a mixture of the super-absorbent polymer particles having a relatively high absorption rate and the super-absorbent polymer particles having a relatively low absorption rate. In this case, two different types of super-absorbent polymer particles must be mixed with the fluff pulp fibers as homogeneously as possible. Here arises another problem that a significant difference in specific gravity between the super-absorbent polymer particles and the fluff pulp fibers makes it difficult to mix them to a desired homogeneity. The sandwich type core including the layer of aggregated super-absorbent polymer particles, on the other hand, is accompanied with a problem that the super-absorbent polymer particles readily form the gel block as these polymer particles absorb body fluids and a certain amount of body fluids stagnates above the gel block. The amount of body fluids stagnating above the gel block may flow back toward a sanitary napkin or a diaper wearer's skin and the super-absorbent polymer particles may function in the reverse way when a body weight of the wearer is exerted upon such core. In consequence, a remarkable rewet phenomenon may occur and give the wearer uncomfortable feeling of wetness.